1. Field of the Invention
This invention relates to a pipette device for spotting a sample solution, a reference solution or the like to a slide type ionic activity measuring device, a slide type dry colorimetric liquid analysis device, or the like.
2. Description of the Prior Art
Qualitative or quantitative analysis of a specific chemical constituent in a liquid sample is a general procedure conducted for a variety of industrial purposes. Quantitative analysis of chemical constituents or physical constituents in body fluids such as blood or urine is particularly important in biochemistry and clinical medicine.
In recent years, as disclosed in, for example, Japanese Patent Publication No. 53(1978)-21677 and Japanese Unexamined Patent Publication No. 55(1980)-164356, there has been developed and put into practice a slide type dry colorimetric liquid analysis device for quantitatively analyzing a specific chemical constituent or a specific physical constituent contained in a sample solution simply by spotting a droplet of the sample solution. In order to analyze a chemical constituent or the like contained in a sample solution by use of the slide type dry colorimetric liquid analysis device, a measured amount of the sample solution is applied to a chemical analysis slide and is incubated for a predetermined time in an incubator to cause a color reaction, and the reflection optical density is measured with a wavelength selected in advance in accordance with the combination of the constituent of the sample solution with a reagent contained in the reagent layer of the chemical analysis slide. In this manner, it is possible to achieve quantitative analysis of the chemical constituent or the like.
Also, as disclosed in, for example, Japanese Unexamined Patent Publication Nos. 58(1983)-211648 and 59(1984)-30055 and Japanese Patent Application No. 59(1984)-11744, there has been proposed an ionic activity measuring device for receiving an aqueous liquid sample, for example, wine, beverage, service water, or, a body fluid (blood, urine, saliva or the like), which is provided in droplets and quantitatively analyzing the activity or concentration of a predetermined ion contained in the sample by potentiometry.
In general, the ionic activity measuring device is provided with at least one pair of ion selective electrodes having as the outermost layer an ion selective layer which reflectively responds to a predetermined ion. The ion selective electrode pair is supported between an upper frame and a lower supporting frame. The upper frame is provided with a pair of liquid access holes positioned to correspond to the position of the ion selective electrode pair. A porous bridge (which is preferably constituted of twisted yarn) is disposed, usually on the upper frame, for achieving liquid junction and thus electrical conduction, between a sample solution put to one of the pair of the liquid access holes and a reference solution put to the other of the pair. In the case where multiple pairs of the ion selective electrodes are provided, pairs of porous liquid distributing members for communicating pairs of ion selective electrode pairs with pairs of the liquid access holes are disposed generally between the upper or the lower frame and the ion selective electrode pairs.
In the case where the ionic activity measuring device having the aforesaid configuration is provided with, for example, three pairs of ion selective electrodes responding respectively to Na.sup.+, K.sup.+, and Cl.sup.- ions, a reference solution having known activity values of these ions is spotted to one of the pair of the liquid access holes, and a sample solution wherein the activity values of these ions are unknown is spotted to the other of the pair of the liquid access holes (the reference solution and the sample solution should preferably be spotted substantially at the same time). The reference solution and the sample solution, on one hand, penetrate through the porous liquid distributing members to the corresponding ion selective electrodes. On the other hand, the reference solution and the sample solution penetrate through the porous bridge until they contact each other near the middle of the porous bridge to achieve liquid junction, and thus electrical conduction is effected between the two solutions. As a result, a potential difference proportional to the difference in a activity of each ion between the reference solution and the sample solution arises between the electrodes of each ion selective electrode pair. When the potential differences are measured, it is possible to measure the activity values of the Na.sup.+, K.sup.+ and Cl.sup.- ions contained in the sample solution simultaneously, sequentially or, when necessary, based on measured values and calibration curves determined in advance from the activity values of the ions in the standard solution (by use of the Nernst equation).
With the aforesaid ionic activity measuring device, it is possible to measure the ionic activity simply by spotting the sample solution and the reference solution only once. Therefore, the ionic activity measuring device is very advantageous for analysis of an aqueous liquid sample, particularly for clinical analysis of a sample such as of blood taken from the human body.
When chemical analysis using the aforesaid ionic activity measuring device, the slide type dry colorimetric liquid analysis device or the like is carried out, it is necessary to feed a predetermined amount of a sample solution, a reference solution or the like by spotting. As the spotting means for this purpose, a pipette device is used.
The pipette device comprises, for example, a vertical housing with a cylindrical portion formed at least at the lower part of the housing, a piston member slideably disposed in the housing and the lower end portion of which is urged upwardly, and a pipette tip fitting section arranged at the lower end of the housing so that the pipette tip fitting section communicates with the cylindrical portion. In order to feed a sample solution, a reference solution or the like with the pipette device, a pipette tip is fitted to the tip fitting section, the tip is dipped into the solution, and the piston member is moved up in the cylindrical portion to draw the sample solution or the like into the pipette tip. Then, the lower end of the pipette tip is moved into position over the slide etc. for spotting, and the piston member is pushed down by a finger or the like to spot the sample solution or the like onto the slide etc.
In this case, the sample solution or the like spotted onto the slide etc. is not immediately absorbed thereinto, and remains for some time in spherical droplet form thereon. However, in many cases, spotting is conducted by positioning the lower end of the pipette tip close to the slide for accurately spotting the sample solution or the like at a predetermined position on the slide. Therefore, the lower end of the pipette tip often may contact the sample solution spotted in the spherical droplet form, and if the piston member is then released and thereby moved upward by the urging force, the sample solution or the like spotted to the slide is drawn back into the pipette tip.
Therefore, in order to feed a sample solution or the like by use of the aforesaid pipette device, it is necessary to keep the piston member pushed down, move the pipette device up to separate the lower end of the pipette tip from the spotted liquid on the slide, and then release the piston member. However, the piston member is often pulled up by error before taking up the pipette device away, causing drawing back of the liquid into the pipette tip.